Chain tensioners in engines are used to control the power transmission chains as the chain travels around a plurality of sprockets. The slack of the chain varies as the temperature in an engine increases and as the chain wears. When a chain wears, the chain elongates and the slack in the chain increases. The increase in slack may cause noise, slippage, or tooth jumping between the chain and the sprocket teeth. If the increase of the slack of the chain is not taken up, by a tensioner for example, in an engine with a chain driven camshaft, the engine may be damaged because the camshaft timing is misaligned by several degrees due to slippage or tooth jumping.
The performance of a hydraulic tensioner is based on two primary functions of a check valve. First, oil must flow through a check valve and into a high pressure chamber of the tensioner as the piston extends to take up chain slack. If the flow restriction of the check valve is too great, the piston will not have enough oil volume to support its extended length. Secondly, as the chain begins to push the piston back into the tensioner the oil wants to flow back out of the check valve. At this point the check valve ball must move back to seal off the oil passage. If the response time is to slow it takes longer to build up the necessary pressure to support the piston and chain control becomes an issue.
Hydraulic tensioner check valves have been previously disclosed in U.S. Pat. No. 7,404,776; U.S. Pat. No. 7,427,249; and U.S. Published Application No. 2008/0261737. Current singular check valve ball technology is limited in its ability to provide variable flow. This technology has two methods of increasing flow. The first option is to increase the diameter of the ball which increases the conical flow area between the seat and ball. The adverse effect of increasing the ball diameter is that the balls mass also increases. As the mass of the ball increases the response time to reverse the direction of the ball to seal off the inlet aperture also increases. The second method of increasing the flow is to increase the travel of the ball. Allowing the ball to move further away from the seat will increase the conical flow area, but it also means response time will increase. Neither of these methods provide variable flow.
Ball check valves have been previously disclosed in U.S. Pat. No. 1,613,145; U.S. Pat. No. 2,308,876; U.S. Pat. No. 4,018,247; and U.S. Pat. No. 4,253,524. These non-analogous patents pertain to a casing string of an oil well, a high speed gas compressor, and high pressure reciprocating oil well pumps. While the earliest of these patents was issued in 1927, known hydraulic tensioners have not included a variable flow ball check valve for a timing chain or timing belt assembly. It is believed that this lack of adaptation is due to the difficulty in designing a cost effective package to contain and control a plurality of balls in a small, compact, lightweight configuration.